The present invention relates to an optical monitor module that launches a portion of light emitted from an optical fiber into another optical fiber for propagation therethrough to a monitoring part.
In a conventional optical monitor module, light emitted from an optical fiber is launched into an optical waveguide on an optical waveguide substrate having formed thereon an optical branching circuit, and light branched by the optical branching circuit is emitted from the optical waveguide substrate for incidence on a monitoring section. This prior art is disclosed, for instance, in Japanese Patent Application Kokai Publications Nos. 2001-358362 and 347665/94.
With such a conventional type of optical monitor module which monitors the light branched by the branching circuit of the optical waveguide formed on the optical waveguide substrate, light of relatively large power needs to be branched for monitoring because of a propagation loss by the optical waveguide. Further, the optical branching circuit has a Y-branch configuration and the two optical waveguides are formed substantially at right angles to each other—this leads to the defect of relatively much space being occupied by the optical waveguide substrate. One possible solution to this problem is an optical module configuration in which no branching circuit of the optical waveguide is used but instead light emitted from an optical fiber is launched into a beam splitter through space and light transmitted through or reflected by the beam splitter is launched into another optical fiber for propagation to the monitoring part. This module structure does not suffer a loss of light resulting from the propagation through the optical waveguide, but since the optical fibers and the beam splitter are spaced relatively wide apart, the light beam diverges (that is, the beam diameter increases), resulting in an increase in the light loss. Further, the two optical fibers are disposed substantially at right angles to each other, occupying much space.